Hydraulically driven equipment, such as a lawn tractor, have had transaxle structure mounted in a housing including a drive input connection, a gear reduction drive, and oppositely-extending differentially-connected axles, and a hydrostatic transmission is connected to the exterior of the housing whereby a drive output from the hydrostatic transmission connects to the drive input to the transaxle structure.
The known prior art structures have not integrated the hydrostatic transmission with the transaxle components in a common housing to provide a common sump and with the use of a unique center section between the hydraulic components of the hydrostatic transmission as disclosed herein.
A hydrostatic transmission has a pair of hydraulic displacement units with fluid connections therebetween. In a typical hydrostatic transmission, the hydraulic displacement units each have a rotatable cylinder block mounting a plurality of reciprocal pistons and with the piston-receiving chambers in the cylinder block communicating with ports for fluid flow to and from the piston-receiving chambers. Many different types of structure are known for achieving fluid communication between the arcuate ports associated with the pair of rotatable cylinder blocks. Such structure can be by means of tubing or by means of a structural section with fluid passages and positioned adjacent both rotatable cylinder blocks. This structural section can be either integral with a housing for the hydrostatic transmission or a separate component mountable between the hydraulic displacement units and separable from the housing.
A prior art hydrostatic transmission has a pair of hydraulic displacement units generally in side-by-side relation and with a rotatable cylinder block of each of the hydraulic displacement units being associated with a structural section having arcuate ports for association with both of the hydraulic displacement units. A pair of generally parallel straight passages, formed in the structural section intersect and communicate with the arcuate ports in pairs whereby there is fluid communication between a pair of arcuate ports associated one with each of the hydraulic displacement units.
The prior art also includes hydrostatic transmissions wherein the hydraulic displacement units are disposed at a selected fixed angle relative to each other whereby the axes of rotation of the rotatable cylinder blocks thereof are at an angle to each other and a structural section disposed therebetween has had a pair of faces at the selected angle whereby arcuate ports associated therewith may coact with the angularly-related cylinder blocks of the hydraulic displacement units.